Basic set-up of a 3com 4500 managed network switch

I’m a PHP developer by trade with a strong Linux background. One thing that has been lacking from my skill set is how networking really works.

In an effort to rectify this, I bought myself a 2nd hand managed network switch from ebay. A 26 port (24 x 10/100mb + 2 x 1gb) “3com SuperStack 3 Switch 4500”.

Flashing lights and noisy fans, I feel like I’m headed in the right direction.

First things first – can I plug it into my router (with DHCP), have it get an IP address and log into the web interface?

No ūüôĀ

Using nmap to sweep the subnet, that the router manages, returned no results for the known MAC address of the switch.

Even checking the router for connected devices didn’t list the known MAC address of the switch.

If I wasn’t getting into the system via the network, I would have to use the console port instead.

As I didn’t have a null modem cable to hand, and I don’t have an active machine with a d9 serial port, I grabbed something from Amazon:¬†¬†(NB: does not work with this switch, keep reading)

As I’m a Linux user, I would be playing with /dev/ttyUSB0. And to use that, my user has to be in the dialout group:

Connecting to the serial console should be easy with:

Hooked up the cable, ran the command to bring up the serial interface and switched on the switch.

This, annoyingly vertical, video shows that something happens (watch the green block skit around in the black window) but no text appears:

Every different program I tried (screen, minicom, putty) to connect to the device all resulted in the same output.

Thanks to fellow 3com switch owner Intrbiz, I have been able to borrow a known working cable.

Hooked up between the PC and switch, ran the byobu-screen command and turned on the switch – It lives!

Now that I have a way of talking to the switch, I can configure it in a way so that I don’t need the console cable (as much).


Factory reset (this requires the console cable):

We need to factory reset for the following reasons:

  • remove any unknown users
  • restore the admin password to the factory default
  • remove any network configuration set-up by the previous owners
  • set-up our own network configuration

Start a console session and power on or reboot the switch.

  • Hit ctrl+b when prompted. Be quick, you don’t get long.
  • Now in the boot menu, tell the switch to ignore the saved configuration for the next reboot (option 7).
  • Reboot the switch (option 0).

Let it boot normally and wait until something like this appears:

  • Hitting enter will log you in as the admin user.

  • Hit enter again to put your cursor on a new line, not at the end of the debug output line.¬†Enter “save” to save the default configuration over the configuration that was written by the previous owner.

It’s now safe to reboot or power cycle the switch as much as you like and it’ll have the factory default settings.


Assign a static IP address to the network switch (this requires the console cable):

  • Ensure that the switch has booted and then connect to the console

  • Enter the system view

  • Switch to vlan 1

  • Set an IP address followed by netmask

  • Set the default route for the switch

  • Return to the user view

  • Save the configuration


Enable SSH login (this requires the console cable):

  • Ensure that the switch has booted and then connect to the console

  • Enter the system view

  • Create the public SSH key

  • Configure the authentication mode

  • Enable the SSH protocol for inbound connections

  • Exit the interface configuration and return to the system-view

  • Create a new user for our SSH connections

  • Set the user’s password

  • Give the user SSH access

  • Exit back to the system view

  • Allow the user to login via SSH using their password

  • Exit back to the user view

  • Save the configuration

  • Check that the SSH login works


Enable Web login (this can be done with the console cable or an SSH session to the switch):

  • Connect to the switch via the console
  • Change to the system view

  • Switch to the admin user

  • Configuration stuff

  • Return to the user view

  • Save the config changes




Enabling SSH logins:

Fixing the web login:

Vagrant hostsupdater plugin without having to enter your sudo password

Vagrant – Great

Hosts Updater plugin – very handy

Having to enter your sudo password when the plugin edits your hosts file – really annoying.

I finally got around to addressing this on my dev system. Looking at the plugin source there are two sudo commands that we need to cater for. One to add hosts and one to remove.

Adding the following to my sudoers file worked a treat:

There are a couple of things to address when you add this to your own sudoers file:
1. Change ‘iain’ to your own user name
2. ‘sed’ might be running from a different path. You can find out by running: which sed

Getting your news when it has become olds

When something really note worthy happens, I usually don’t go longer than a few days without knowing.

But, for some reason, I just learnt about something that happened 19 March 2008.

Only by reading this comic in this book did I learn of Arthur C. Clarke‘s passing. This is particularly shocking as Arthur C. Clarke was the main author of the books I read in my childhood.

You’d have thought that it would have been bigger news.¬†¬† Maybe I just live under a rock.

Buy the book, read the comics, follow the might of Hijinks Ensue.

Fireworks – fun or explosives for all?

[this is a bit of a random rant, excuse me whilst I ramble]

Every year, the sale of fireworks seems to come earlier and earlier.

In the UK, we used to use them on the 5th November (or the closest weekend). Now they seem to be in use from the 30th October to mid November. And then over the whole Christmas period.

When in the right hands, they can be great fun. But as people have more and more access to them, the fun becomes less.

My thoughts:

  • The sale of fireworks should be licensed in the same manner as the sale of alcohol.
  • The purchase of fireworks should be more tightly controlled. Get them out of the supermarkets and corner-shops for a start.
  • The use of fireworks should also be licensed. This would restrict displays to organised events and not 14 year old kids throwing fireworks down the street, or scaring fish.

I don’t want to be kill joy, but explosives need to be treated with respect.

Maybe I’m getting old and jumpy. I love the look of a good display. I don’t like having to fish the cat out from underneath the bed.